What a difference a few bubbles make! Sparkling wine starts out as still wine and then undergoes a second fermentation. More carbon dioxide is formed — but this time, it's captured and not allowed to escape.

There are many sparkling wines: Cava (from Spain); Prosecco and Asti (from Italy); Sekt (from Germany); blanc de noir (from the Pinot Noir grape); blanc de blanc (from the Chardonnay grape) — and, the most famous, Champagne.

Not all sparkling wines are Champagne. In order to legitimately be called Champagne, a sparkling wine must meet the following criteria. It must:

• Be produced in the Champagne district of France.

• Be produced from the Chardonnay, Pinot Noir, and/or Pinot Meunier grapes grown there.

• Get its bubbles via the méthode champenoise (Champagne method).

The Champagne method is an expensive and labor-intensive means of naturally carbonating a wine. First, wine is made from local grapes. This is no easy feat. The vineyards of Champagne lie so far north that ripeness is an issue in most years. After clarification and a measure of aging, the wine is put into thick Champagne bottles, along with enough yeast and sugar to initiate a second fermentation. It is this second fermentation in the tightly sealed bottle that puts the bubbles in the bubbly. The carbon dioxide can't get out, so it's dissolved in the wine.

The wine is aged — sometimes for years — along with the dead yeast that accumulates as sediment. The trick is to get rid of the sediment without losing all the bubbles. By gradually tilting the bottle a little bit each day until it is inverted, the dead yeast is coaxed into the neck of the bottle where it can quickly be removed. At that time, the bottle is topped off and adjusted for sweetness and then immediately corked so that the wine doesn't lose its effervescence.

The Champagne method, because it's so time-consuming and labor-intensive, is expensive — one reason for the high price tag of good Champagne. Sparkling wines that are carbonated in other, cheaper ways can be sold for much less.